ArcPy and ArcGIS – Geospatial Analysis with Python

By Silas Toms

About This Book

• Perform GIS analysis faster by automating tasks, such as selecting data or buffering data, by accessing GIS tools using scripting
• Access the spatial data contained within shapefiles and geodatabases, for updates, analysis and even transformation between spatial reference systems
• Produce map books and automate the mapping of geospatial analyses, reducing the time needed to produce and display the results

Who This Book Is For

If you are a GIS student or professional who needs an understanding of how to use ArcPy to reduce repetitive tasks and perform analysis faster, this book is for you. It is also a valuable book for Python programmers who want to understand how to automate geospatial analyses.

• Language: English
• Publisher: Packt Publishing
• Release date: Feb 26, 2015
• ISBN: 9781783988679

Book preview

Table of Contents

ArcPy and ArcGIS – Geospatial Analysis with Python

Credits

About the Author

About the Reviewers

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Why subscribe?

Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Downloading the color images of this book

Errata

Piracy

Questions

1. Introduction to Python for ArcGIS

Overview of Python

Python as a programming language

Interpreted language

Standard (built-in) library

The glue language

Wrapper modules

The basics of Python

Import statements

Variables

For loops

If/Elif/Else statements

While statements

Comments

Data types

Strings

Integers

Floats

Lists

Tuples

Dictionaries

Iterable data types

Other important concepts

Indentation

Functions

Keywords

Namespaces

Zero-based indexing

Important Python Modules for GIS Analysis

The ArcPy module

The Operating System (OS) module

The Python System (SYS) module

The XLRD and XLWT modules

Commonly used built-in functions

Commonly used standard library modules

Summary

2. Configuring the Python Environment

What is a Python script?

How Python executes a script

What is the Python interpreter?

Where is the Python interpreter located?

Which Python interpreter should be used?

How does the computer know where the interpreter is?

Make Python scripts executable when clicked on

Integrated Development Environments (IDEs)

IDLE

PythonWin

Aptana Studio 3

IDE summary

Python folder structure

Where modules reside

Using Python's sys module to add a module

The sys.path.append() method

Summary

3. Creating the First Python Script

Prerequisites

ModelBuilder

Creating a model and exporting to Python

Modeling the Select and Buffer tools

Adding the Intersect tool

Tallying the analysis results

Exporting the model and adjusting the script

The automatically generated script

File paths in Python

Continuing the script analysis: the ArcPy tools

The Intersect tool and string manipulation

The string manipulation method 1–string addition

The string manipulation method 2–string formatting #1

The string manipulation method 3–string formatting #2

Adjusting the Script

Adding the CSV module to the script

Accessing the data: Using a cursor

The final script

Summary

4. Complex ArcPy Scripts and Generalizing Functions

Python functions–Avoid repeating code

Technical definition of functions

A first function

Functions with parameters

Using functions to replace repetitive code

More generalization of the functions

Summary

5. ArcPy Cursors – Search, Insert, and Update

The data access module

Attribute field interactions

Update cursors

Updating the shape field

Adjusting a point location

Deleting a row using an Update Cursor

Using an Insert Cursor

Inserting a polyline geometry

Inserting a polygon geometry

Summary

6. Working with ArcPy Geometry Objects

ArcPy geometry object classes

ArcPy Point objects

ArcPy Array objects

ArcPy Polyline objects

ArcPy Polygon objects

Polygon object buffers

Other Polygon object methods

ArcPy geometry objects

ArcPy PointGeometry objects

Summary

7. Creating a Script Tool

Adding dynamic parameters to a script

Displaying script messages using arcpy.AddMessage

Adding dynamic components to the script

Creating a Script tool

Labelling and defining parameters

Adding data types

Adding the Bus Stop feature class as a parameter

Adding the Census Block feature class as a parameter

Adding the Census Block field as a parameter

Adding the output spreadsheet as a parameter

Adding the spreadsheet field names as a parameter

Adding the SQL Statement as a parameter

Adding the bus stop fields as a parameter

Inspecting the final script

Running the Script Tool

Summary

8. Introduction to ArcPy.Mapping

Using ArcPy with map documents

Inspecting and replacing layer sources

Fixing the broken links

Fixing the links of individual layers

Exporting to PDF from an MXD

Adjusting map document elements

Automated map document adjustment

The variables

The map document object and the text elements

The layer objects

Replacing the data sources

Adjusting layer visibility

Generating a buffer from the bus stops feature class

Intersecting the bus stop buffer and census blocks

Populating the selected bus stop and buffer feature classes

Updating the text elements

Exporting the adjusted map to PDF

Running the script in the Python Window

Summary

9. More ArcPy.Mapping Techniques

Using arcpy.mapping to control Layer objects

Layer object methods and properties

Definition queries

Controlling the data frame window extent and scale

Adding a Layer object

Exporting the maps

Summary

10. Advanced Geometry Object Methods

Creating a Python module

The __init__.py file

Adding advanced analysis components

Advanced Polygon object methods

Generating random points to represent population

Using the functions within a script

Creating an XLS using XLWT

Summary

11. Network Analyst and Spatial Analyst with ArcPy

The Network Analyst extension

Using Network Analyst

Creating a Feature Dataset

Importing the datasets

Creating the Network Dataset

Accessing the Network Dataset using ArcPy

Breaking down the script

The Network Analyst module

Accessing the Spatial Analyst Extension

Adding elevation to the bus stops

Using Map Algebra to generate elevation in feet

Adding in the bus stops and getting elevation values

The final result

Summary

12. The End of the Beginning

Getting field information from feature classes

Accessing the ListFields' properties

List comprehensions

Creating the field information functions

Querying feature class information

Generating File Geodatabases and feature classes

Generating a feature class

Setting up the script tool parameters

Environmental settings

Resolution and tolerance settings

Summary

Index

ArcPy and ArcGIS – Geospatial Analysis with Python

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ArcPy and ArcGIS – Geospatial Analysis with Python

Copyright © 2015 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: February 2015

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Credits

Author

Silas Toms

Reviewers

Alessio Di Lorenzo

Dara O'Beirne

Mark Pazolli

Marjorie Roswell

Commissioning Editor

Ashwin Nair

Acquisition Editor

Harsha Bharwani

Content Development Editor

Akashdeep Kundu

Technical Editor

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Copy Editors

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Project Coordinator

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Proofreaders

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Indexer

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Production Coordinator

Alwin Roy

Cover Work

Alwin Roy

About the Author

Silas Toms is a geospatial programmer and analyst with a love of geography, history, food, and sports. He resides in the San Francisco Bay Area and can't decide which side of the Bay is more beautiful. He received a bachelor's degree in Geography from Humboldt State University and is currently pursuing a master's degree in GIS at San Francisco State University. With a background in GIS analysis for city governments and environmental consulting, Silas loves the combination of GIS and Python for analysis automation and data manipulation.

Working for Arini Geographics, Silas is helping governments understand how GIS can organize and simplify the management of infrastructure and the environment. This dual role as a programmer and analyst allows him to use Python and GIS to quickly produce geospatial data and tools. Combined with web mapping, these tools are transforming how governments work to serve the public. He also teaches workshops on ArcPy and web mapping at the City College of San Francisco, while hoping to one day finish his master's thesis.

Silas has worked as a reviewer on the book Python Geospatial Analysis, Packt Publishing and is working on the book Python Geospatial Development, Packt Publishing to be published in 2015.

I would like to thank my girlfriend, Christine, for her encouragement and patience. I would like to thank my boss, Gabriel Paun, for his inspiration and for pushing me to become a true GIS professional. I would like to thank the faculty at HSU and SFSU for their help along the way, and I would like to thank my family for their belief in me and for never asking me if I was going to become a teacher with my geography degree (even though I have and I love it!).

About the Reviewers

Alessio Di Lorenzo is a marine biologist and has an MSc in Geographical Information Systems (GIS) and Remote Sensing. Since 2006, he has been dealing with the analysis and development of GIS applications dedicated to the study and spread of environmental and epidemiological data. He is experienced in the use of the main proprietary and open source GIS software and programming languages.

Dara O'Beirne is a certified GIS Professional (GISP) with over eight years of GIS and Python experience. Dara earned both his Bachelors and Masters of Arts degrees in geography from San Francisco State University. Dara is currently a GIS Analyst working at Arini Geographics in Santa Clara, CA. Before joining Arini Geographics, Dara was a GIS Analyst and technical lead at Towill Inc., a GIS and Land Surveying company in Northern California. At Towill, Dara played a central role in developing and implementing procedures related to the collection and analysis of LiDAR data for environmental and engineering applications. Prior to Towill, Dara gained his professional GIS experience working for the Golden Gate National Recreation Area managed by the National Park Service, one of the largest urban park systems in the world, which includes National treasures, such as Alcatraz, Muir Woods, and the Marin Headlands. His Master's Thesis examined the errors associated with measuring tree heights in an urban environment with both traditional field methods and airborne LiDAR data.

I would like to thank my wife, Kate, and daughter, Anya O'Beirne, for their patience and assistance during the review of this book.

Marjorie Roswell is a web developer and map maker from Baltimore, MD. She purchased her first GIS in 1991, and built an application to assist citizen callers to the Baltimore Office of Recycling. Recent projects include interactive maps of legislative scores, political endorsements, committees, election data, and advocacy interests.

Her site http://committeemaps.org/ details Congressional committee membership, while the site http://farmbillprimer.org/ is devoted to mapping and charting federal food and farm policy.

Marjorie is the author of Drupal 5 Views Recipes, Packt Publishing. She was the technical reviewer of jQuery UI 1.10, The User Interface Library for jQuery, Packt Publishing.

Mark Pazolli is an engineer and data scientist who uses ArcGIS and Python to help his employers decipher the mountains of data they keep on the assets of the Western Australian electrical network. He has qualifications in Electrical Engineering, Computer Science, and Applied Mathematics. He appreciates excellent design and enjoys building interesting things.

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Preface

ArcGIS, the GIS software from industry leader ESRI, allows for the analysis and presentation of geospatial data.

The integration of Python into ArcGIS has made the ArcPy module an important tool for GIS students and professionals. The ArcPy module provides a powerful way to improve productivity when performing geospatial analysis. From basic Python scripting through advanced ArcPy methods and properties, ArcPy and other Python modules will improve the speed and repeatability of any GIS work flow.

This book will guide you from basic Python scripting to advanced scripting tools. It focuses on geospatial analysis scripting and touches on automating cartographic output. By the end of this book, you will be able to create reusable modules, add repeatable analyses as script tools in ArcToolbox, and export maps automatically. By reducing the time-consuming nature of GIS from days to hours, one GIS professional can become as powerful as a whole team.

What this book covers

Chapter 1, Introduction to Python for ArcGIS, offers a quick introduction to the basics of Python, including other uses for the programming language. It covers Python data types and important modules used throughout the book.

Chapter 2, Configuring the Python Environment, is an introduction to how Python works: its folder structure, executables, and modules. It also explains importing modules into scripts, the built-in modules, and covers Integrated Development Environments (IDEs), which are powerful programming aids.

Chapter 3, Creating the First Python Script, demonstrates how to use ArcGIS ModelBuilder to model the first analysis and then export it as a Python script. String manipulations and how to use file paths in Python are also introduced.

Chapter 4, Complex ArcPy Scripts and Generalizing Functions, examines how to perform analyses and produce outputs that are not possible using ModelBuilder. By using functions, or reusable code blocks, repeating code is avoided.

Chapter 5, ArcPy Cursors – Search, Insert, and Update, covers ArcPy data access cursors and how they are used to search, update, or insert records in feature classes and tables. It explains the quirks of iterating using cursors, and how to only select or update the records of interest.

Chapter 6, Working with ArcPy Geometry Objects, explores ArcPy Geometry objects and how they are combined with cursors to perform spatial analysis. It demonstrates how to buffer, clip, reproject, and more using the data cursors and the Arcpy geometry types without using ArcToolbox.

Chapter 7, Creating a Script Tool, explains how to make scripts into tools that appear in ArcToolbox and are dynamic in nature. It explains how the tools and scripts communicate and how to set up the ArcTool dialog to correctly pass parameters to the script.

Chapter 8, Introduction to ArcPy.Mapping, explores the powerful Arcpy.Mapping module and how to fix broken layer links, turn layers on and off, and dynamically adjust titles and text. It shows how to create dynamic map output based on a geospatial analysis.

Chapter 9, More ArcPy.Mapping Techniques, introduces Layer objects, and their methods and properties. It demonstrates how to control map scales and extents for data frames, and covers automated map export.

Chapter 10, Advanced Geometry Object Methods, expands on the ArcPy Geometry object methods and properties. It also explains how to create a module to save code for reuse in subsequent scripts, and demonstrates how to create Excel spreadsheets containing results from a geospatial analysis.

Chapter 11, Network Analyst and Spatial Analyst with ArcPy, introduces the basics of using ArcPy for advanced geospatial analysis using the ArcGIS for Desktop Network Analyst and Spatial Analyst Extensions.

Chapter 12, The End of the Beginning, covers other important topics that need to be understood to have a full grasp of ArcPy. These topics include the Environment Settings, XY values and Z and M resolutions, Spatial Reference Systems (Projections), the Describe functions, and more.

What you need for this book

You will need the proprietary or free version of ArcGIS 10.1/10.2/10.3. To support your environment, you will need 2GB RAM, 32-bit or 64 bit machine hardware configuration, and Windows 7/8. Python 2.7 is required to do the programming and is installed along with ArcGIS.

Who this book is for

This book is intended for GIS students and professionals who need an understanding of how to use ArcPy to